The breathing in of oxygen produces carbon dioxide as a “waste gas”. Carbon dioxide is an odorless gas that occurs naturally in air in a very small proportion of 0.03 vol %. Higher carbon dioxide contents in the surrounding air have an unfavorable physiological effect on humans. As small a concentration as 0.5 vol % CO2 in the surrounding air produces typical symptoms such as headache, which is why the maximal workplace concentration of CO2 is set at 0.5 vol % (5000 ppm).
In closed air conditioned spaces, for example, it is desirable to be able to regulate the carbon dioxide content in the air wherein excess CO2 is continuously removed from the air.
Moreover, lowering the CO2 content can be advantageously combined with additional measures to improve the room climate, for example, by enrichment of the room air with oxygen as well as air conditioning.
Conventional oxygen enrichment methods for improvement of the air quality in closed air circulation systems and rooms or cabins are mostly based on pure oxygen enrichment devices such as for example pressure swing adsorption systems or hollow fiber membrane systems. Exemplary corresponding devices are described in U.S. Pat. Nos. 4,867,766; 5,890,366; 6,427,484; 5,158,584 and 4,896,514.
Some of the prior art devices identified above provide conditioning of the oxygen-enriched air. Systems have also been proposed (e.g. German Patent 195 45 764) which remove carbon dioxide with adsorbers. This technology however has the disadvantage of also simultaneously dehumidifying the air. The consequence is either very costly adsorber regeneration with hot air or vacuum as well as a separate humidification of the room air, or disposal of the used adsorber cartridges, which makes the corresponding systems uneconomical for most applications.
In order to avoid the disadvantageous physiological effects of carbon dioxide enrichment in room air stated above there is a demand for suitable methods and devices which make possible a depletion of the carbon dioxide content in room air, and can if necessary simultaneously climatize or enrich the air with oxygen.
Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention.